The present invention relates to power returnable coilable rules, and more particularly, to connections between the coilable rule and the power spring.
Power returnable coilable rules have enjoyed considerable success in the marketplace and are very widely employed. Generally, such rules have a power spring providing the retracting force to draw the metal rule inwardly of the casing and effect its coiling thereabout. In some such rules, the spring operates to effect rotation of a reel to which its outer end is connected, and it is not directly connected to the inner end of the blade; and the inner end of the blade is also connected to the reel. In other rules, there is direct engagement between the inner end of the blade and the outer end of the spring.
Since it is generally possible to pull the rule outwardly from the housing sufficiently to draw the outer end of the spring through the exit aperture in the casing, the end of the spring may abut the wall of the casing about the exit aperture causing a force to be exerted upon the connection to the rule which can effect disengagement. Moreover, the tension forces on the interengageable elements which normally comprise a tongue and some form of aperture in which the tongue is seated, also have a tendency to produce disengagement when the rule is withdrawn fully or excessively from the casing.
It is an object of the present invention to provide an improved power returnable coilable metal rule in which there is a novel and secure interengagement between the outer end of the spring and the inner end of the coilable rule.
It is also an object to provide such a coilable metal rule in which the elements may be economically fabricated and readily assembled to provide such secure engagement between the rule and spring.
Another object is to provide such coilable rule in which the rule and power spring may be readily assembled by automated procedures.